Wireless communication and mobile technology are quite prevalent in modern society, and becoming more so all the time. Millions of people around the world use numerous types of wireless-communication devices to communicate with other communication devices, including other wireless-communication devices, both directly and/or via one or more networks. In a typical arrangement, a user interacts with a portable and mobile wireless-communication device known by terms such as mobile station, mobile subscriber unit, access terminal, user equipment (UE), cell phone, smartphone, personal digital assistant (PDA), tablet, and the like.
Furthermore, such a wireless-communication device typically communicates over a defined air interface with one or more entities of what is known and referred to herein as a radio access network (RAN), which may also be known by terms such as (and/or form a functional part of) a cellular wireless network, a cellular wireless telecommunication system, a wireless wide area network (WWAN), and the like. For illustration and not by way of limitation, the balance of this disclosure uses UEs as example wireless-communication devices and RANs as example wireless-communication systems (i.e., networks) via which the referenced UEs engage in wireless communication. And though many wireless-communication protocols exist, the balance of this disclosure uses Long Term Evolution (LTE) as an illustrative example.
In the context of a given RAN, the entity with which the UE directly communicates over the air interface is known by terms such as base station, base transceiver station (BTS), and the like. In the parlance of LTE and in the balance of this description, this entity is referred to as an eNodeB. The communication link via which data is transmitted from the eNodeB to UEs is known as the downlink, while the communication link via which data is transmitted from UEs to the eNodeB is known as the uplink. And LTE uses different air-interface technologies on the downlink and uplink. In particular, LTE employs a technology known as Orthogonal Frequency Division Multiple Access (OFDMA) on the downlink while employing a technology known as Single Carrier Frequency Division Multiple Access (SC-FDMA) on the uplink.
On the downlink, LTE defines several physical-layer data and control channels. The downlink physical-layer data channels are known as the physical broadcast channel (PBCH), the physical downlink shared channel (PDSCH), and the physical multicast channel (PMCH), while the downlink physical-layer control channels are known as the physical downlink control channel (PDCCH), the physical control format indicator channel (PCFICH), and the physical hybrid-ARQ (automatic repeat query) indicator channel (PHICH). The PDSCH is the primary traffic-bearing channel on the downlink, and is used by the eNodeB to transmit data in the form of downlink transport blocks to the various UEs to which the eNodeB is providing service.
On the uplink, LTE defines three physical-layer channels, known as the physical uplink shared channel (PUSCH), the physical uplink control channel (PUCCH), and the physical random access channel (PRACH). In general, the PUSCH is designated for carrying user data and some control information, the PUCCH is designated for carrying uplink-feedback data (e.g., media access control (MAC) uplink-feedback data) and requests to be scheduled for uplink user-data transmission, and the PRACH is designated for purposes such as initial UE access, service requests (i.e., switching from idle to active mode), and reestablishing uplink synchronization.
In LTE, as is the case with other protocols, certain constructs are defined to promote, among other goals, the reliability and efficiency of wireless communication. One such construct is known as a retransmission scheme (or protocol), which typically involves acknowledgement (and, explicitly and/or implicitly, non-acknowledgement) and timeout mechanisms at one or more layers (e.g., physical, MAC, etc.) of the Open Systems Interconnection (OSI) model (or “stack”). Messages that are sent to acknowledge successful receipt of a certain quantum of data (e.g., a packet, a transport block, or the like) are often known as ACKs, and messages that are sent to indicate failure to successfully receive a certain quantum of data are often known as NACKs (or NAKs), while failure to receive either an ACK or NACK is typically interpreted as a NACK. At the MAC layer, LTE uses hybrid ARQ (HARQ), which employs both ARQ and forward error correction (FEC). At the radio link control (RLC) layer, LTE uses ARQ.
In LTE, UEs are configured such that: (i) at times when they do not have uplink data (a.k.a. user data, user traffic, and the like) to send but do have uplink-feedback data (e.g., ACKs, NACKs, channel quality indicator (CQI) feedback, rank indications, and the like) to send, they send the uplink-feedback data via the PUCCH; and (ii) at times when they have both uplink data and uplink-feedback data to send, they annex (i.e., “piggyback”) the uplink-feedback data to the uplink data and send the combination via the PUSCH. The annexation may involve multiplexing the uplink data and the uplink-feedback data together, though it could just as well involve any other type or types of annexation, such as prepending, appending, and the like.
If enough interference is present on the PUCCH, ACKs sent via that channel may not be successfully received and decoded by the eNodeB, which would typically then behave as if it had received a NACK, by retransmitting the corresponding downlink transport block(s). As will be appreciated by those of skill in the relevant art, the effective throughput on the downlink is reduced by such unnecessary retransmission, perhaps not only for that UE but quite possibly also for one or more other UEs arranged to use shared air-link resources. As such, there is a need for a method and an apparatus for mitigating PUCCH interference in LTE systems.
Those having skill in the relevant art will appreciate that elements in the figures are illustrated for simplicity and clarity, and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help to improve understanding of various embodiments. Furthermore, the apparatus and method components have been represented where appropriate by conventional symbols in the figures, showing only those specific details that are pertinent to understanding the disclosed embodiments so as not to obscure the disclosure with details that will be readily apparent to those having skill in the relevant art having the benefit of this description.